Address for Correspondence

Transcription

1 Gupta, et al., International Journal of Advanced Engineering Research and Studies E-ISSN Proceedings of BITCON-015 Innovations For National Developent National Conference on : Leading Edge Technologies in Electrical and Electronics Engineering Research Paper RELIABILITY STUDY OF SMALL GENERATION MICRO HYDRO POWER ijay Prakash Gupta 1, ishwanath Prasad Kuri, Ait Agrawal 3 Address for Correspondence 1, M.Tech Scholar, 3 Assistant Professor Dr. C..Raan University, Bilaspur, CG India ABSTRACT This paper presents the perforance of isolated 3-phase self-excited induction generator (SEIG) in icro-hydro power plant using water pup as load. The daily electrical load profile in reote ountainous region or area shows vast difference in iniu and axiu load on the generator operated in isolated ode. Induction generators are ost suitable types of generators for renewable energy conversion systes due to their advantages over conventional generators. The load on these generators has to be kept constant to aintain the voltage and frequency under perissible liits. Therefore under off-load conditions, the extra energy available can be utilized for other purposes such as operating water pup water heater and other need based applications rather than wasting the energy in resistive dup load. In this proposed work, the potential benefits of using water pup as load under light/off-load conditions have been explored. KEY WORDS:- SEIG, ELC, ballast. I. INTRODUCTION Distributed power generation has received greater attention in recent years for use in reote and rural counities due to the cost and coplexity of grid systes with related transission losses and reduced reliability. Thus, suitable stand-alone systes using locally available energy sources have becoe a preferred option. With increased ephasis on ecofriendly technologies the use of renewable sources such as sall hydro, wind and bioass is being explored. Subject to availability, sall hydro systes with inial civil works to energize local counities are considered attractive. As these systes are located in reote areas, they ust be robust, reliable, econoical and anageable by local counities: this applies to the prie over, generator and associated controllers. Micro turbines or pups as turbine are used as prie overs. The squirrel cage induction generator in self-excited ode is found to be the ost suitable option as generator due to advantages such as low cost, siple construction, ruggedness, brushless rotor, absence of DC source, aintenance-free nature, self-protection against short circuits and off-the shelf availability. The self-excited induction generator has a ajor drawback of poor voltage regulation. The inherent poor voltage regulation of the SEIG is due to the difference between the reactive power supplied by the excitation capacitors and that deanded by the load and the achine. This is a ajor bottleneck of its application in isolated ode. Prie Mover SEIG Consuer load Capacitor Bank Fig.1.1: Scheatic of SEIG connected to consuer load The generated voltage of the SEIG depends upon the speed, excitation capacitance, load current and power factor of load. Aong various renewable energy Int. J. Adv. Engg. Res. Studies/I/II/Jan.-March,015/ based power systes, ini/icro hydro power schee eploys an uncontrolled turbine which aintains the constant input of hydro power. The use of governor for input control is not an econoical option due to its cost and operational aintenance. One way to regulate the voltage and frequency of SEIG is to aintain a constant load at its terinals. Under such operation, SEIG requires fixed capacitance for excitation resulting in a fixed-point of operation. For this purpose, a suitable control schee is to be developed such that the load on SEIG reains constant deste the change in the consuer load. Also, such control schee should be siple, econoical, rugged, and reliable. The power output is kept constant by connecting an auxiliary or dup load in parallel with the consuer load such that the total generated power is held constant. The application of load controller to SEIG syste is a siple and cost effective approach to regulate the voltage and frequency but the load controller does not copensate for variable reactive power deand. In this work, only resistive loading has been done which does not require variable reactive power copensation i.e. fixed capacitive excitation can be used. Harnessing the renewable energy sources for electric power generation is an area of research interest and nowadays the ephasis is being laid on the cost effective utilization of these resources for quality and reliable power supply. Traditionally, synchronous generators have been used for power generation, but induction generators are increasingly being used these days to harness renewable energy resources because of their relative advantageous features. These features include aintenance and operational siplicity, brushless and rugged construction, lower unit cost, good dynaic response, self-protection against faults and ability to generate power at varying speed. Also, the induction generator does not require separate DC exciter and its related equipent like field breaker, rheostat and autoatic voltage regulator and therefore requires less aintenance. These advantages facilitate induction generator operation in stand-alone/ isolated ode or in parallel with synchronous generator for supplying local load and in grid ode. In reote locations or hilly areas, a icro-hydro syste with unregulated low head turbines, which aintain alost constant input power

2 Gupta, et al., International Journal of Advanced Engineering Research and Studies E-ISSN due to fixed head and discharge coupled with selfexcited induction generator ay be one of the ost suitable option for supplying local loads. Figure 1. shows a tycal scheatic of icro hydro-power syste. II. ELC SEIG SYSTEM Electronic load controller (ELC) is the cobination of an uncontrolled rectifier, a filtering capacitor, chopper, and a series dup load (resistor). The scheatic diagras of ELC SEIG systes are shown in Fig. 1.3 for supplying three-phase loads. The uncontrolled rectifier converts the SEIG ac terinal voltage to dc. The uncontrolled rectifier output has the ripples, which should be filtered and, therefore, a filtering capacitor (C) is used to soothen the dc voltage. An IGBT is used as a chopper switch. A suitable gate driver circuit has been developed that turns on the chopper switch when the consuer load on SEIG is less than the rated load and turns off the chopper switch when consuer load on the SEIG is at a rated value. When the chopper switch is switched on, the current flows through the dup load and consues the difference power (generated power-consued power) which results in a constant load on the SEIG and, hence, constant voltage and frequency at the load. Fig.1.:. Scheatic of icro hydro-power syste III. WORKING The SEIG ELC syste consists of a three-phase delta-connected induction generator driven by an uncontrolled Pico hydro-turbine and an ELC. Suitable valued capacitors are connected across the SEIG such that it generates rated terinal voltage at full load. Since the input power is nearly constant, the output power of the SEIG is held constant at Fig.1.3: Scheatic diagra of ELC-SEIG syste varying consuer loads. The power in surplus of the consuer load is duped in a resistance through the ELC. Thus, SEIG feeds two loads in parallel such that the total power is constant, that is where is the generated power of the generator (which should be kept constant), is consuer load power, and is the dup load power. P out =P d + P c (1.1) Fig 1.4: Basic principle of Electronic Load Controller Int. J. Adv. Engg. Res. Studies/I/II/Jan.-March,015/ Fig. 1.5 Division of power between consuer and ballast load

3 Gupta, et al., International Journal of Advanced Engineering Research and Studies E-ISSN I. METHODOLOGY The voltage and current equations of induction generator in stationary dq reference frae are given as ds qs dr qr K1[ vds Rsids ( L ) Rridr wr ( L ) iqs wr Li qr] 1 qs Rsiqs ( L ) Rriqr wr ( L ) ids wr Li dr K [ v K [ ( Rr ) idr ( L /LsLr ) vds ( L /LsLr ) Rsids wr ( L ) iqs wriqr K [ ( R /L ) i ( L /L L ) v ( L /L L ) R i ] w ( L /L ) i ] (1.3) w i r r qr s r qs s r s qs r r ds r dr (1.1) (1.) (1.4) where p represents the derivative with respect to tie and Ls Lls L ; Lr Llr L ; K1 [1/( Ls ( L / Lr )] ; K [1/(1 L / L L )] ] s r The SEIG operates in saturation region and its agnetizing current can be calculated in ters of stator and rotor currents as I (( ids idr ) ( iqs iqr ) (1.5) The agnetizing inductance (L ) is function of agnetizing current (I ).and is given as L / I (1.6) Where is agnetic flux linkage. The Figure 1.6 shows the relation between applied voltage and agnetizing current (I ) while induction otor under study is driven at synchronous speed X and X C are per phase agnetizing and capacitive reactance; I s, I r, I L are per phase stator, rotor and load currents; g is air gap voltage and a, b are per unit frequency and speed. Rotor paraeters are referred to stator and all reactance are at base frequency. Fig.1.8. Steady state equivalent circuit of SEIG with a balanced load For the circuit shown in Fig.1.9, the loop equation can be written as IZ=0. Since under steady state condition I 0, it follows that Z=0; i.e., Fig 1.6: The air gap voltage and agnetizing current at synchronous speed. Fro the synchronous speed test data and active power absorbed by the achine, a polynoial function of fourth order curve fitting relation is established as shown in Figure 1.7 which describes the nonlinear relation between agnetizing reactance and current given as g 3 AX BX CX D F (1.7) Where A=-0.10, B=9.3, C= and D= The shaft torque of the prie over is considered as a function of speed and given as: T shaft ( K1 K wr ) (1.8) Where, K 1 and K are the prie over coefficients given in Appendix-A. Fig1.7. Nonlinear relation between air gap voltage and agnetizing reactance DETERMINATION OF EXCITATION CAPACITOR Figure 1.8 shows the per phase equivalent circuit of three phase SEIG with load where R 1, X 1, R, X are per phase stator and rotor resistances and reactance; (1.9) (1.10) Equating the real and iaginary parts of (1.10) separately to zero and siplifying, it can be shown that, b= a+ = a+ (1.11) Fro (1.11), equating {M /M 1 } ={N /N 1 } and siplifying, a quadratic equation can be arrived at with capacitive reactance, X c as the variable. Then, Xc = {-K ± K - 4K 1 K 3 }/K 1 (1.1) the values of K 1, K, K 3, M 1, M, N 1 and N are given in Appendix A. A generator will stay in self-excitation for a given load and speed only within a given range of terinal capacitance i.e., C in and C ax. At these two boundary values, the agnetizing reactance of the generator will reach the highest value called critical agnetizing reactance (X c ). Putting X = X c in (1.10) for a given achine, the values of X c corresponding to C in and C ax can be obtained. In (1.1), positive sign taken for the discernent of quadratic equation, leads to C in and negative sign gives C ax. Thus,(1.1) can be solved for X c for any required per unit frequency, a. Then using the base frequency taken, the value of capacitances, C in and C ax can be calculated. A Matlab progra has been ade to find the value of iniu capacitance. Int. J. Adv. Engg. Res. Studies/I/II/Jan.-March,015/

4 Gupta, et al., International Journal of Advanced Engineering Research and Studies E-ISSN Fig.1.9 ariation of excitation capacitance with terinal voltage and power factor Appendix- A D 1 = X 1 + X, D = X + X, D 3 = R+R 1 D 4 = X+X 1, D 5 =R 1 +R, D 6 =RX 1 +R 1 X D 7 = -a R D D 6 a x x [RD 5 a xx 1 ] D 8 = AR (R D 1 +X D 3 +XR ) D 9 = R (arr 1 R a 3 R XD 1 a 3 X D 6 ) D 10 = a[r D D 4 +X X (D 3 +R )] D 11 = a[rr 1 R D a XX X D 5 + a X 1 (RX X R XD )] D 1 = a [R R D 6 +RR X D 5 a XX 1 X R ] M 1 = X C (R D D 3 a X X D 4 ) +D 7 M = X C D 8 +D 9 N 1 = X C D 10 +D 11 N = X C (-R R D 3 + a R X D 4 ) + D 1 K 1 = D 8 D 10 + R R D D 3 a R X D 4 (R D D 3 + R X D 3 -a X X D 4 ) K = D 8 D 11 + D 9 D 10 R D D 3 D 1 + a X X D 4 D 1 +R R D 3 D 7 a R X D 4 D 7 K 3 = D 9 D 11 D 7 D 1 DUMP LOAD DESIGN The DC output voltage of rectifier is given by: 3 LL DC (1.3505)LL (1.3505) π (1.13) where, LL is the rs value of the output voltage of the SEIG and the input voltage of the diode bridge rectifier. Taking an over voltage 10% of rated ac voltage for transient condition, the peak DC voltage is given as: DC, peak The AC input current is calculated as: (1.14) I AC P LL (1.15) where, P is the rated power output for SEIG. Taking distortion factor of 0.9 and crest factor of 1.8, then AC peak input current to diode rectifier is: IAC, peak 1.8 IAC / A (1.16) The axiu voltage and current ratings are and 7 A respectively. Coercially available rating of diodes for single phase rectifier and IGBT chopper switches are selected of 900 and 15 A. The dup load resistance is given by: R D ( DC A ) / P ( ) / Ω Int. J. Adv. Engg. Res. Studies/I/II/Jan.-March,015/

5 Gupta, et al., International Journal of Advanced Engineering Research and Studies E-ISSN (1.17) The value of filtering capacitor (C f ) is selected on the basis of ripple factor (RF) and given by the relations as: C f {1/(4 f R D )}[1 {1/( RF)}] for 15 % ripple factor, filtering capacitor is: (1.18) C f {1/( )}[1 {1/( 0.15)}] = μ F (1.19) A nearest coercially available value of 470 μf is taken as filtering capacitor. RESULT AND DISCUSSION A three phase 3.73 kw, 30, 13 A, 50 Hz, 1500 rp delta connected squirrel cage induction achine is used as a self-excited induction generator. The electronic load controller (ELC) is designed for 1600 kw resistive load. On application of resistive load, load current increases and dup load current decreases so that power transfers fro dup load to consuer load and SEIG experiences constant load on it. The ELC is connected fro the starting of SEIG.The terinal voltage reains constant on changes in load.the frequency also reains constant with the change of resistive load. REFERENCES [01] E.D. Bassett and F.M. Potter, Capacitive excitation of induction generator,aiee Trans. Elect. Engg., ol.54, pp , [0] Chan T.F., Capacitance requireent of induction generators, IEEE Trans. on Energy Conversion, ol. 8, No., pp , [03] Chan T.F., Perforance analysis of a three-phase induction generator connected to a single-phase power syste, IEEE Trans. on Energy Conversion, o. 13, No. 3, pp , [04] Chan T.F., Steady state analysis of self-excited induction generator, Electric Machines and Power Systes, ol. 3, No., pp , [05] Chan T.F., Steady state analysis of self-excited induction generator using an iterative ethod, IEEE Trans. on Energy Conversion, ol. 10, No. 3, pp , 1995 [06] A. K. Al Jabri and A. I. Aloha, Capacitance requireent for isolated self-excitedinduction generator, Proc. Inst. Elect. Eng. B, vol. 137, no. 3,pp , May [07] M.Senthil Kuar, N.Kuaresan, R.Karthigaivel and M.Subbiah, Deterination of boundary values of excitation capacitance and iniu load ipedance for wind-driven SEIGs, [08] N.Tutkun and F.Arslan, Deterination of capacitance range in the self-excited induction generator through the hybrid genetic algoriths, [09] B. Singh, S. S. Murthy, and S. Gupta, Analysis and Design of Electronic Load Controller for Self-Excited Induction Generators, IEEE Trans. on Energy Conversion, ol.1,no.1, pp.85-93, March 006. [10] B. Singh, S.S. Murthy, and S. Gupta, Analysis and ipleentation of an electronic load controller for a self-excited induction generator, IEE Proc.-Gener. Trans. Distrib., ol. 151, No. 1, pp.51-60, Jan [11] Elder J.M.,Boys J.T. and Woodward J.L., Integral cycle control of stand-alone generators, IEE Proc., Generation, Transission and Distribution, ol. 13, No., pp , [1] Juan M. Rairez, and Eanuel Torres M., An electronic load controller for self-excited induction generator, [13] Bonert R., Hoops G., Stand-alone induction generator withterinal ipedance controller and no turbine controls, IEEE Trans. on Energy Conversion, ol. 4, No. 1, pp. 8-31, 1990 [14] Bonert R., Rajakaruna S., Self-excited induction generator with excellent voltage and frequency controls, IEE Trans. on Energy Conversion, ol. 5, No. 1, pp , [15] Singh Bhi, Murthy S.S. and Gupta Shara, A voltage and frequency controller for self-excited induction generators, Electric Power Coponents and Systes, ol. 34, pp , 006. [16] ChatterjeeJayanta K., enkatesaperual B. and Reddy Gopu Naveen, Analysis of operation of a self-excited induction generator with generalizedipedance controller, IEEE Trans. on Energy Conversion, ol., No., pp , June 007. [17] Singh Bhi, KasalGaurav, oltage and frequency controller for isolated asynchronous generators feeding 3-phse 4-wire loads, Proc. of the IEEE International Conference on Industrial Technology, pp , 006. [18] Singh B., Shilpakar L. B., Analysis of a novel solid state voltage regulator fora self-excited induction generator, IEE Proc., Generation, Transission and Distribution, ol. 145, No. 6, pp , [19] Bansal R.C., Three-phase self-excited induction generators: an overview, IEEE Trans. Energy Convers., ol. 0, No., pp. 9 99,005 [0] Dheeraj Kuar Palwalia, Analysis and Control of Stand Alone Generator, Ph.D. Thesis, IIT Roorkee,009 [1] M. Godoy Sioes and Felix A.Farret, Renewable Energy Systes Design analysis with Induction Generators. [] Karl Johan Astro and Tore Hagglund, PID controllers: Theory, Design, and Tuning, nd ed. Note: This Paper/Article is scrutinised and reviewed by Scientific Coittee, BITCON-015, BIT, Durg, CG, India Int. J. Adv. Engg. Res. Studies/I/II/Jan.-March,015/